A report expected this week from the International Atomic Energy Agency -LRB- IAEA -RRB- has Israel abuzz with talk of the potential for a pre-emptive strike on Iran 's nuclear facilities .

Western diplomats have told CNN that the report says Iran has mastered the critical steps necessary to design and build a nuclear weapon .

Missiles are not , of course , the only way to launch an attack .

Iran 's nuclear facilities are under siege from cyber attacks . And one , the Stuxnet virus , was able to penetrate Iran 's Natanz nuclear facility , researchers say .

How did it work ?

Stuxnet was stealthy . The Natanz computer network is a closed system , separated from any other network or internet access . So , Stuxnet infected a third party first , likely a trusted contractor to the Natanz facility . That contractor may then have unknowingly passed on the virus by plugging in an infected removable drive into the computers inside the Natanz facility .

More importantly , Stuxnet was smart . It knew exactly what it was looking for : A specific software called Step 7 used specifically to run the Siemens controllers operating at Natanz .

Stuxnet spread through the network undetected . If it did n't find the Step 7 software , it left things alone . But once it found its target , Stuxnet set to work .

First , it effectively hijacked the Natanz control system , speeding up or slowing down the centrifuges , wearing them out prematurely .

As the centrifuges destroyed themselves , Stuxnet sent back signals that everything was fine and running smoothly . So , the operators may not have known this was happening until it was too late .

So , just how effective was Stuxnet ?

According to the Institute for Science and International Security , IAEA records show that between the end of 2009 and early 2010 about 1,000 centrifuges at Natanz had to be replaced . Stuxnet is the suspected culprit .

Still , that 's only about one out of every nine centrifuges and , despite a minor dip in production , uranium enrichment continued apace .

Who created Stuxnet is still a mystery . Many computer security researchers believe the virus is so complex and sophisticated that it would have needed the resources of a nation state -- or a combination of states -- to produce it .

Researchers at internet security firm Symantec say they have identified a new virus called Duqu that they believe is a successor to Stuxnet , although not all security experts agree .

`` This is not a copycat , '' insists Orla Cox of Symantec . `` Whoever created this had access to the same source code as Stuxnet . ''

Cox says Duqu is , at this stage , a malware designed simply to spy and collect information from Iran 's computer systems , but she suspects it may be ultimately intended for sabotage .

`` It could be that Stuxnet did n't entirely achieve what was wanted the first time around , '' Cox told CNN .

Duqu was released as late as August 2010 , just after the Stuxnet virus had done its damage , stunning many researchers who had not expected to see another virus of the same complexity released so quickly .

Ralph Langner , the German computer security specialist credited with discovering Stuxnet , says it does n't matter who created Duqu . The problem , he says , is that Stuxnet , in its bid to stop nuclear proliferation , may have sparked its own arms race .

`` The first cyberwar weapon is comparable to the first nuclear weapon , '' he wrote in a blog post recently . `` To build the first nuclear bomb , it took a genius like Oppenheimer and the resources of the Manhattan project . To copy the design , it requires just a bunch of engineers -- no genius needed .

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Israel abuzz with talk of potential for pre-emptive strike on Iran 's nuclear facilities

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Western diplomats say IAEA report says Iran able to design and build nuclear weapon

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Iran 's nuclear facilities have also come under attack from cyber attacks

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One such attack by Stuxnet virus able to penetrate Iran 's Natanz nuclear facility